1. Field of the Invention
The present invention generally relates to an image forming apparatus having a transport unit with a guide unit. More specifically, the present invention relates to a guide unit having a guide plate that transports sheets, a transport unit having a guide unit, and an image forming apparatus having a transport unit.
2. Background Information
Normally an image forming apparatus such as a printer, fax, or photocopier, includes an image forming unit in which toner images are formed and the toner images are transferred onto sheets, a fixing unit in which the transferred toner images are fixed to the sheets, and so on.
The image forming unit includes a photosensitive drum, a charging unit that charges the surface of the photosensitive drum, a light exposure unit that forms electrostatic latent images by decharging part of the charged area of the photosensitive drum, a developing unit that forms toner images based on the electrostatic latent images, a transfer unit that transfers the toner images onto sheets, a cleaning unit that cleans the surface of the photosensitive drum, and so on.
The transfer unit transfers toner images formed on the photosensitive drum onto sheets transported between the photosensitive drum and the transfer unit by applying a bias voltage to the transfer unit with a polarity opposite to that of the toner.
Here, to transport the sheets between the photosensitive drum and the transfer unit, a guide plate is disposed on the upstream side of the transfer unit in the direction of transport of the sheets, and the sheets are transported along the guide plate.
If a guide plate manufactured from resin is used, the guide plate can become charged as a result of friction with the sheets, and if dust adheres to the guide plate, defective sheet transport or defective toner transfer can be caused by this dust.
Therefore, as disclosed for example in Japanese Laid-open Patent Application No. H11-184269, a grounded metal guide plate is used to prevent charging of the guide plate.
Here, if a grounded metal guide plate is used in highly humid environments the resistance value of the sheet is reduced, and transfer current from the transfer unit can flow to the guide plate through the sheet. Therefore, under this type of environment the toner image may not be sufficiently transferred to the sheet, and transfer defects can occur.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved image forming apparatus having a transport unit with a guide unit. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.